Functional Programming

A teaser

A type system

A type system is a tractable syntactic method for proving the absence of certain program behaviors by classifying phrases according to the kinds of values they compute.

Система типов — это гибко управляемый синтаксический метод доказательства отсутствия в программе определенных видов поведения при помощи классификации выражений языка по разновидностям вычисляемых ими значений.

Types and Programming Languages
Benjamin C. Pierce
2002

Static vs Dynamic,

Strong vs Weak

... PROFIT?

Guarantees
Code coverage
Modelling the domain
Compilation to native code
Powerful run-time system

Still have to test though...

And prototyping can be painful.

data DisplayAccounts
  = DisplaySingle AccountInfo
  | DisplayMulti [AccountInfo]

Python

Any namedtuple can be accidentally compared to any other with the same number of fields.

@dataclass
class InventoryItem:
    '''Class for keeping track of an item in inventory.'''
    name: str
    unit_price: float
    quantity_on_hand: int = 0

-- | Class for keeping track of an item in inventory.
data InventoryItem =
  InventoryItem
    { name :: Text
    , unitPrice :: Double
    , quantityOnHand :: Int
    }